Process for the reclamation of bichromates.



ensures W. TUCKER, on 2:02am nunovnn, mnlssnonusnrrsessmnon or ONE-HALF c To 'rnomes sidnnnnnu', on Lynn, MASSACHUSETTS. c

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To all whom it may concern:

Be it known that 1, Cinemas W. Tuonnn, a citizen of the United States, residing at North Andover, in the county. of Essex and State of Massachuetts, have invented a certoihnew and useful Improvement in Procasses for the Reclamation of Bichromatcs,

' of which the following ise specification.

Ill

Clfhisinvention perteins-to en improved process for the reclamation and saving of i the unused excess of sodium or potassium 1 bichromate from Waste liquor baths resultskitus or hides,

ing from the practice of various processes,

eudmore particularly the reclamation and saving of said substances from baths em' ployed in the process of chrome tsnning of This bichromate in solution forms an important ingredient in the bath inwhioh the skins are soaked. as one of the steps of the tanning process, it is 'neces I s'ary thaten excess of bichromateshould be supplied in the bath in order that enough of the substance required for tanning may be absorbed by the skins and a large amount is left in the liquor When'the skins are re moved. This excess cannot be used in such condition and the result has been that prior to the. development of my invention it has been looked upongencially' is a Waste.

product,-=a.nd thrown away. In fact,-only about one-half o-f-the sodium or potassium bichrornete used in the two bath tanning process of. chrorneleether can be effectively used, and the remainder, has been Wasted. The larger the cannery, the greater, of

course, the Waste, .and as. both sodium bi- ,el romete and potassium, bichromat-e are all) comparatively expensive, the loss of'so much of the substances during aday IS a verysecrious tem. y

. .I am aware that etteinpts have been made to utilize the refuse'liquor from the bath, and a so to conv'ertrthe cbroinetes 1n the Waste into lead chromate for use in other arts, but none of such attempts have, so far asl have beeneble to ascertain, been satis- Specificetion 0t Letters'Petent. Patented Get. 17, 191 6. npplicetion'filcd Mei-ch 25, 1916 Serial No. 8 6370. I

ing the basis of the present invention mcy Y be said, preferably, toinvolve the following steps: First, neutralization of theWaste.

bath With an alkaline agent though this is not absolutelycssential under certain circumstances; second, clarifying the bath by mechanically removing the suspendid, for eign matters, this being e'fiected by introducing into the bath aclerifying agent which acts to harry or throw down the finely-suspended dirt, or by filtering the liquid; third, the addition of a suitable 'material, as a soluble carbonate, to precipitate any alkaline earth which may be'present, but this step is not essential; fourth, evaporation to a suitable point or degree of concentration for the removal of those salts which are less soluble than the chromates. or bichr'omates; fifth, acidification, ifnecessary for' transformation of the normal chromates-to "bichromates in those instances Where the bath is or has been made alkaline.

The first step is not absolutely essential, I though preferable, this primarily for the reason that if the Wasteliquor has been rens dered alkaline the second step maybe more readily carried out, and the fourth step, that of evaporation, may then be/carried out in a metal evaporator; So, too, if the liquor be acid when evaporated, it is not necessary to add acid as the fifth step to reform the bichromates. In performing the first step of the process, I introduce-potassium cai'bonate or sodium carbonate or ammonia, or

other suitable alkaline agent, or it may be the same material Which isused to form the clarifying substance of the second step.

Usually this neutralization is necessary, as With'the materials preferably employed in the next step-thebath must be in an alkaline state. Moreover, it is desirable that the both should be in an alkaline condition .et the time of evaporation as it would be objectionable to evaporate a'n'ac'id bath in a metal evaporator, which is commonly used.

e I. v In performing or carrying out the second step, that of clarification, I prefer to place or produce in theliquor a suitable clarifying agent Which is preferably, though not necessarily, aluminum hydrate. Thebath, after the skins have been taken from it, contain salts left" from the other steps of the tanning" process, dirt from the skins, lime salts and variousother impurities, and I'find that by the introduction of aluminum hydrate the BEST AVAILABLE cop bath is efiiciently clarified. It removes, by mechanical action, all of the insolublematter (however fine) in the liquor, and carries it to the bottom of the tank. It does not remove the lime or other salts, but this is accomplished later.

The aluminum hydrate may be prepared outside the clarifying tank and added during stirring of the neutralized liquor, or an aluminum salt may be added, to the li uor and then an alkaline agent introduce to produce the aluminum hydrate in .the liquor.

In some tanning processes and in connection with one in which my process has been s' isuccessfully employed, aluminum sulfate has already been brought into the bath by a treatment of the skins with such material previous to their introduction into the chrome bath, and the aluminum hydrate may be recipitated by-a suitable alkaline agent, suc as caustic soda, carbonate of soda, etc.

lithe-aluminum sulfate be not present, as

just indicated, it may be introduced and followed. up by the substances above mentioned to bring about the formation of aluminum hydrate. While I prefer aluminum'hydrate as the clarifying agent, other materials .may be employed, such as calcium phosphate, chromium hydrate, silica or silicic acid. The material employed must be flocculent and as it settles in the bath it acts to carry down with it the finely-suspended dirt and foreign matter. Silica or silicic acid may be" used without first neutralizing the bath and evaporation could'take place without thenecessitycf adding acid to reform the bichromate. Any of the materials might be added directly to the bath or formed therein as above indicated in con- 40 motion with the aluminum hydrate.

The second step, orthat of clarification .of the liquor, which as above noted may take place at. the outset without preliminar neu tralization, may likewise be effected y filtering the liquor instead of employing a flocculent agent to entrain the materials held in suspension as above set forth. In other words the act of filtering, or of entraining the matter held in suspension are in effect the same, producin a mechanical separation or gatherin of the undissolved and suspended foreign matters from tlieli r.

Afterclarification is effected b eit-'er of the foregoing methods, andv t e' cleared liquor is drawn oil, the removal of the alka line earths, as lime and magnesia," isefiected, when necessary or desirable; This is done b precipitation brought about through the a dition' of a suitable carbonate, such as sodium or potassium carbonate. The preci itate thus formed is allowed to settle and t e liquor drained ofi. e

The next step, or that of ,eva oration of the cleared and softened liquor, 1s then carried out to effect a separation of thosalts suitable pomt of.concentratio ordinary temperature. vThe resultant to 1 separate less which .r. 1858' soluble a... the alkali 'chromates or bichromates. This-isbest carried process of treatment which the liquor has undergone, its state of acidity has been 7 changed so that it is more alkaline than bichromates. This' is preferably" accom' plished by the addition of sulfuric acid, 35' though other acids may be used; X. Crystallization takes place when the But ficiently concentrated solution containing either of the bichromates is cooled tothe' 'l" tals may then be further purified by reso 11- I 'tion in boiling water and recooling, when very pure crystals are obtained. The resid ual liquor in each case is then added to the next body of liquor to be evaporated, and 96 so continued, so that there is no low of the bichromates.

It will, of course, be appreciated that the concentrated and filtered liquor, properly acidified to bring about the reformation of the bichromates, may be directly employed in the tanning baths without going through I. the step of-crystallization, as 'ust specified, and the subsequent step of 'ssolving the bichromate crystals. I

Having thus described my invention, what I claim is: g p 1. "The method of recovering sodium or potassium bichromate from s nt liquors containing said materials, whicli consists in removing suspended impurities therefrom;.

removing alkaline earths from such clarified liquor by thslntroduction of an Lllma line carbonate and'thereby causing a. pre cipitation of the alkaline earths; and evaporating the liquor thus cleared and softened. 1

soluble saltsthan the bichromates.

2. The method of recovering sodium or potassium bichromate 'from nt li uors containing such substanoesQw 'ch oonsists in removing suspended impurities'therein by the action of aluminum hydrate; thereafter eifecting aprecipitation of the alkaline earths containedin the liquor; evaporating 125 the liquor thus treated to remove by crystallization the low soluble materials contained in the liquor; and finally adding such quantity of acid as is ry toreform the bichromates, v

. use

3. A method of producing sodium or potassium bichromate, Which consists in taking a Waste tanning liquor; removing solid suspended impurities by a mechanical clearing action; removing alkaline earth salts by chemical action; removing salts of less sol ubility than the bichromate by concentration and oversaturation; and regaining the bichromate in crystalline form 'or concentrated solution.

4:. The method of recovering sodium or potassium bichromate from spent tanning the solution of the alkaline earths therein; evaporating the resulting solution to efiect a crystallization of the less-soluble materials contained therein; and finally adding acid to -efiect a reformation of the bichromates.

5. The method of producing sodium or potassium bichromate from spent liquors containing such substances, which consists in mechanically gathering and thereby removing foreign matters held in suspension therein, and thereafter evaporating the iquor to remove the less soluble salts thererom. a

In testimony whereof I have signed'my name to this specification. v

CHARLES W. TUCKER. 

